Project Summary/Abstract This competitive renewal application is designed to test three new hypotheses about the role of excessive oxidative stress and calmodulin kinase II (CaMKII) in pathological responses to myocardial infarction (MI) and aldosterone (Aldo). These studies will use new genetic mouse models developed by us where the activity of mitochondrial CaMKII, oxidized CaMKII (ox-CaMKII) and methionine sulfoxide reductase A (MsrA), the enzyme that reduces and inactivates ox-CaMKII, are controlled. Each of the inter-related, but independent aims is backed by strong preliminary data. Aim 1 Determine how Aldo and ox-CaMKII promote cardiac rupture after MI. We will determine if Aldo increases the frequency of post-MI rupture by enhancing NADPH oxidase and ox-CaMKII, and unravel a previously unknown pathway where ox-CaMKII drives myocardial matrix metalloproteinase 9 (MMP9) expression by HDAC4/5 phosphorylation and MEF2 derepression. Aim 2 Determine the role of ox-CaMKII in myocardial hypertrophy. CaMKII contributes to myocardial hypertrophy, but the potential role of the ox-CaMKII pathway in myocardial hypertrophy is unknown. We will test the novel concept that myocardial ox-CaMKII coherently promotes transcription of matrix remodeling (in Aim 1) and hypertrophic gene programs (in Aim 2) by HDAC4/5 phosphorylation and MEF2 derepression. Aim 3 Determine the role of ox-CaMKII in the transition from hypertrophy to heart failure. Our preliminary studies indicate that CaMKII is resident in mitochondria and that mitochondrial ox-CaMKII plays a decisive role in mitochondria membrane permeability transition pore (mPTP) opening and cell death. We predict that mitochondrial-targeted CaMKII inhibition will significantly delay and mitochondrial-targeted CaMKII over-expression will significantly hasten development of heart failure.